1. Field of the Invention
The present invention relates to an electronic device for serially transferring data using a serial ATA (ATA attachment) interface. More particularly, it relates to an electronic device and signal amplitude automatic adjustment method utilizing a serial ATA interface suitable for automatically adjusting the amplitude of a serial data signal, output to a serial ATA bus, in light of the signal attenuation of the serial ATA bus.
2. Description of the Related Art
At present, standards for serial ATA interfaces as a new type of interface for use in disk drives are now being worked out. Serial ATA interfaces are used as an interface between a peripheral device, represented by a magnetic disk drive, and a host (host system) represented by a personal computer. In this point, serial ATA interfaces are similar to conventional ATA interfaces (i.e., parallel ATA interfaces).
A peripheral device with a serial ATA interface, such as a magnetic disk drive (hereinafter referred to as an “HDD”), is connected to a host by a serial bus. In such an HDD, to secure compatibility with an ATA interface, it is necessary to convert an ATA interface into a serial ATA interface, and convert a serial ATA interface into an ATA interface. Such interface conversion is performed by, for example, an LSI (bridge LSI) called a serial ATA bridge.
In the serial ATA interface standards, three layers of different functions, i.e., a physical layer, link layer and transport layer, are defined. The physical layer has a function for executing high-rate serial data transmission and reception. The physical layer interprets received data, and transmits the data to the link layer in accordance with an interpretation result. The physical layer also outputs a serial data signal to the link layer in response to a request therefrom. The link layer supplies the physical layer with a request to output a signal. The link layer also supplies the transport layer with the data transmitted from the physical layer. The transport layer performs conversion for operations based on the ATA standards. Assuming that the above-mentioned bridge LSI is used in an HDD, the role of the transport layer corresponds to the role of the ATA signal output unit of a conventional host that utilizes ATA connection. The bridge LSI is connected to the disk controller (HDC) of the HDD via an ATA bus (or a bus compliant with the ATA bus) based on the ATA interface standards. Accordingly, in the connection between the bridge LSI and HDC of the HDD, operations equivalent to those stipulated in the ATA interface standards or compatible with the standards are performed. In this case, the portion of the HDD excluding the bridge LSI (hereinafter referred to as a “main HDD unit”) regards the bridge LSI as an apparatus (host) for issuing a command to the main HDD unit. Accordingly, the main HDD unit operates in the same manner as a conventional HDD utilizing ATA connection. Thus, the serial ATA interface is compatible with the ATA standards concerning protocols such as logical commands. However, a data signal (parallel data signal) processed by a parallel ATA interface must be converted into a serial data signal.
The serial ATA interface standards stipulate that a cable with a length of 1 m, at maximum, can be used for data transfer using a serial ATA interface. Further, the serial ATA interface standards sets the maximum and minimum amplitudes of a signal at the receive side to 600 mV and 325 mV, respectively. Actually, however, when apparatuses are connected using a serial ATA interface, attenuation in a data signal due to the cable (serial ATA bus) used must be considered. That is, a data signal output from a transmitter that uses a serial ATA interface attenuates while passing through the cable (serial ATA bus). As a result, the amplitude of the data signal is inevitably reduced when it is received by a receiver. Thus, when the amplitude of a signal output from a transmitter is determined so that at the receive side, it falls within the range stipulated in the serial ATA interface standards, attenuation due to the cable must be considered.
Assume here that the amplitude of a signal output from a transmitter is set in light of maximum signal attenuation that occurs when a cable of 1 m is connected between the transmitter and receiver, so that at the receive side, it falls within the standard range. Assume also that the transmitter is actually connected to the receiver by a very short cable (serial ATA bus). In this case, the attenuation of a signal due to the cable is smaller than the assumed maximum attenuation, therefore the actual signal amplitude at the receiver is higher than in the maximum signal attenuation case. As a result, the amplitude of a signal received may well be higher than the reference (standard) value, which may adversely influences the receiver. On the other hand, if a long cable is used where the amplitude of a signal output from a transmitter is set in light of a short cable, the amplitude of a signal received may be lower than the reference value.
The above-described case where an assumed cable length differs from an actual one can occur when the apparatus to which a serial ATA interface is connected is, for example, a small-size HDD (magnetic disk drive). This is for the following reasons: Firstly, a small-size HDD can be used not only as a storage for a desktop computer, like a large-size HDD, but also as a storage for a portable electronic device, such as a notebook-type personal computer. Thus, a small-size HDD can be used in various occasions. If an HDD is used as a storage for a portable electronic device, the space for the HDD is generally small. In this case, the degree of freedom of selecting the length of a cable connected between the HDD and electronic device is low. For example, if a 2.5-inch HDD is used as a storage for a notebook-type personal computer, the HDD is directly connected to the computer without a cable. Thus, in the case of a small HDD, it is necessary to change the length of the cable used, depending upon the situation. In other words, the cable length cannot be set in advance. This is an example of the above-mentioned case where the assumed cable length differs from the actual one.
Jpn. Pat. Appln. KOKAI Publication No. 2000-341177 (hereinafter referred to as a “prior art document”) discloses an image signal transmission apparatus that allows a user to adjust the amplitude of a signal in accordance with the length of a cable. In this apparatus, when the user activates application software for setting a cable length, a selection dialog box for allowing the user to designate a cable length is displayed. If the user selects a desired cable length from the selection dialog box, an amplitude control command corresponding to the selected cable length is issued. Upon receiving this command, a graphics controller outputs an amplitude control signal corresponding to the command. In response to the amplitude control signal, an amplitude control circuit at a transmit side controls the amplitude of an image signal output from the transmit side to the cable.
As described above, in the image signal transmission apparatus described in the prior art document, the amplitude of an image signal (output signal) output from the transmit side to the cable can be adjusted in accordance with a cable length designated by a user. However, the prior art document merely describes that the amplitude of an image signal is adjusted to a lower one or higher one of two values, depending upon whether 3 m or 10 m is selected as the cable length. In other words, the prior art document does not specify the two values, and does not describe how the adjustment is performed in accordance with the cable length. Accordingly, even if the image signal amplitude adjustment technique (prior technique) described in the prior art document is employed in a system in which electronic devices are connected via serial ATA interfaces, it is still difficult to make the amplitude of an input signal (received signal) at a receive side fall within the range stipulated in the serial ATA interface standards.